It is known that 2-benzyl-5-(4-chlorophenyl)-6-[4-(methylthio)phenyl]-2H-pyridazin-3-one exhibits excellent effect of inhibiting production of interleukin-1β, and is useful as a preventive and therapeutic drug, for example, for immune diseases, inflammatory diseases, and ischemic diseases (Japanese Patent Application Laid-Open (kokai) No. 12-198776). However, this compound has very low solubility in water and exhibits poor dissolution from the preparation. Therefore, a demand has arisen for improvement of its dissolution.
Known techniques for improving the dissolution of a low water-soluble drug include micronization of the drug and preparation of derivatives of the drug. However, micronization does not improve the dissolution of a very low water-soluble drug such as 2-benzyl-5-(4-chlorophenyl)-6-[4-(methylthio)phenyl]-2H-pyridazin-3-one. Meanwhile, when such a drug is prepared into a derivative, the pharmaceutical activity of the drug changes. Accordingly, these techniques are not preferable.
Also, as a technique for improving dissolution, there has been proposed, for example, a method in which a physiologically active substance such as nifedipine is treated with carbon dioxide which is in a supercritical or subcritical state, or with liquid carbon dioxide (e.g., Japanese Patent Application Laid-Open (kokai) No. 2002-302435). This method improves the dissolution of a low water-soluble drug such as nifedipine, but fails to improve the dissolution of a very low water-soluble drug such as 2-benzyl-5-(4-chlorophenyl)-6-[4-(methylthio)phenyl]-2H-pyridazin-3-one.
In view of the foregoing, objects of the present invention are to provide a composition containing a very low water-soluble drug exhibiting improved dissolution, and to provide a method for producing the composition.